The things that intrigue me most about the human body.

[CharonY]

3 hours ago, Lorentz Jr said:

Clothing over smooth skin (A) is better than clothing over hairy skin (B).

Clothing over hairy skin is better than no clothing at all (C).

Not saying that's true, but A>B doesn't disprove B>C.

I think the issue is that it is very easy to make some sort of grand hypothesis in terms of evolution just by conjuring a scenario that somehow provides some kind of selective pressures that seemingly make sense. Things like the aquatic ape hypothesis are rightly criticized because of those. So if we think that we can come up with something better, at lease some level of evidence should be provided that whatever we come up with is in line with what we know (or at least have some sort of evidence).

Fundamentally I find narratives that some species did this and this is why the lost a particular genetic trait problematic, as it conjures the idea that once a species did a thing, it resulted in genetic changes. The reality is the opposite of course. Mutations for hair loss occurred, likely somewhat frequently, but their frequency only increased when they either were not detrimental or became under positive selection.

I was typing the comments below, when I noticed that  joigus provided a similar reference so I am just keeping it brief and just state that the timeline when changes in hair patterns happened predated any evidence of potential tools that could be used for making some sort of warming clothes.

So things like simple shelters or rain protection obviously had low impact on those mutations as all our relatives are still fairly hairy. But what the drivers are to keep hair loss around is still up to debate and as joigus pointed out, far from resolved.

[mistermack]

1 hour ago, Ken Fabian said:

It seems more likely to me that use of clothing was a response to being furless rather than inducing furlessness - a parental response to their furless children suffering from cold perhaps.

But that really makes no sense at all. How did those furless children (and their parents) cope with a downpour, or a cold wet night without a coat of fur? The list of hairless mammals is extremely short, and they are generally very big, like elephants, rhinos and hippos. The list of mammals that are NOT hairless is absolutly enormous. In Africa, a lot of mammals suffer in the heat, but they still retain the fur. Why? Because they need it when the weather turns nasty. 

Our ancestors would have experienced the same problem. How could they evolve hairlessness, without some artificial protection against the elements?

[CharonY]

18 minutes ago, mistermack said:

Our ancestors would have experienced the same problem. How could they evolve hairlessness, without some artificial protection against the elements?

That is a good question and which is why it is necessary to gather information, such as

- what is the timeline of hair loss? Was it rapid, or gradual?

- how much fitness loss is associated with a given loss?

- what kind of protection was feasible at any given point in human development (in terms of tool use and needs, hunting behaviour etc.) and how much of it could it offset the above fittness loss?

- what are the benefits of mutations? If it requires so much effort to counteract its negative effects, why did it became dominant in the first place?

Again, coming into a situation where certain traits are not needed does not make them magically disappear. As noted, the evidence so far to not seem to support the development of clothing before hair loss. I.e. hypotheses need to conform with existing knowledge.

In that regard, persistence hunting was one of the hypotheses that tried to explain benefits of hair loss. I will also note that tentative evidence for man-made fires seem to predate tentative evidence for man-made clothing. Also, I note that the San people referenced earlier often wear very little clothing (up to somewhat recently) so it certainly does not seem to be that detrimental in climates where our ancestors lived.

 

[zapatos]

48 minutes ago, mistermack said:

Our ancestors would have experienced the same problem. How could they evolve hairlessness, without some artificial protection against the elements?

Any number of ways I would imagine.

Perhaps when they were losing hair the elements were not harsh enough to make having hair a significant advantage.

Perhaps a loss of hair eliminated a significant cause of death due to vermin.

Perhaps the loss of hair was a byproduct of a genetic change that enhanced survival to an extent that outweighed hair loss.

Perhaps hyperthermia death outweighed hypothermia death.

I don't think we can just pick one without evidence simply because it sounds good us.

[Ken Fabian]

@mistermackDepends on the climate, surely. Keeping active by day, huddling together by night would do in milder climates. Hominids have been clever tool users and problem solvers for a very long time - even dragging vegetation over themselves can provide insulation. But, yes, clothing and shelter and fire may well have preceded furlessness and made it easier to cope with when it happened and perhaps those were used or known but not used all the time; furlessness could make their use more of a necessity.

But I don't see how they would lead to the evolution of the furless child; where is the selective advantage? I think just not needing fur to keep warm when fur does provide significant benefits - even if not all the time - isn't going to be enough for a species to lose it.

As an aside I've heard it said that hiking in cold, wet conditions without clothes is less likely to result in hypothermia than wearing wet clothes; my own experience hiking in swimming shorts in the rain seems to support that - like swimming, as long as I kept moving I wasn't cold - but I haven't done that outside a mild climate or in extreme conditions.

[Genady]

4 hours ago, Ken Fabian said:

@mistermackDepends on the climate, surely. Keeping active by day, huddling together by night would do in milder climates. Hominids have been clever tool users and problem solvers for a very long time - even dragging vegetation over themselves can provide insulation. But, yes, clothing and shelter and fire may well have preceded furlessness and made it easier to cope with when it happened and perhaps those were used or known but not used all the time; furlessness could make their use more of a necessity.

But I don't see how they would lead to the evolution of the furless child; where is the selective advantage? I think just not needing fur to keep warm when fur does provide significant benefits - even if not all the time - isn't going to be enough for a species to lose it.

As an aside I've heard it said that hiking in cold, wet conditions without clothes is less likely to result in hypothermia than wearing wet clothes; my own experience hiking in swimming shorts in the rain seems to support that - like swimming, as long as I kept moving I wasn't cold - but I haven't done that outside a mild climate or in extreme conditions.

I have a question about the timeline. Weren't humans hairless before they first left Eastern Africa? If they were, what was the climate there when the hair was lost?

Another question is, does fur give a significant benefit to a child? Does it make a difference in surviving childhood? Considering that human children are very fragile and dependent on adult protection in many respects compared to other mammals.

[Genady]

Aren't human babies hairless just as another consequence of being born too soon? 

Quote

Humans are born 12 months too early. Gestation should be 21 months. Humans evolved to become the pre-eminent animal in the world, but our big brain, bipedalism, and small female pelvic outlet have caused us to pay the price of being born too soon with all of its disadvantages.

Humans are born too soon: impact on pediatric otolaryngology - PubMed (nih.gov)

[mistermack]

Imagine you're a lion living in the Serengeti. 

On the hottest days of the year, you see them visibly suffering in the heat, in obvious distress. And yet, they are still wearing a fur coat. They don't need the fur coat for most of the time, but they can't take it off. Why are they put through that ordeal by evolution? It's because on the odd occasion, the weather is so bad that they need a fur coat. Maybe just ten days out of the year, who knows? But ten days in a row might be enough to kill them, or kill their cubs at any rate. So they are forced to suffer in the heat, to be able to see out the worst weather. 

Lion cubs are especially furry, compared to the adults. Because little bodies chill quicker. From an evolutionary standpoint, lose your cubs to bad weather, and you're species is on it's way out.

If only the lions could take the fur coat off when it's roasting hot, and just put it on when it's freezing cold and pissing rain, then they would have the best of both worlds. 

That's what we've achieved by making shelters and using skins, (or whatever is available for covering). You can sit out the worst of it, and then emerge and endure the heat without having to wear a fur coat.

The date of clothing arriving is a bit of a red herring. It's shelter that I'm talking about, whatever the means. Anything that keeps the rain off. Skins, leaves, grasses whatever. Clothes would probably come much later. 

[dimreepr]

1 hour ago, mistermack said:

Imagine you're a lion living in the Serengeti. 

On the hottest days of the year, you see them visibly suffering in the heat, in obvious distress. And yet, they are still wearing a fur coat. They don't need the fur coat for most of the time, but they can't take it off. Why are they put through that ordeal by evolution? It's because on the odd occasion, the weather is so bad that they need a fur coat. Maybe just ten days out of the year, who knows? But ten days in a row might be enough to kill them, or kill their cubs at any rate. So they are forced to suffer in the heat, to be able to see out the worst weather. 

Lion cubs are especially furry, compared to the adults. Because little bodies chill quicker. From an evolutionary standpoint, lose your cubs to bad weather, and you're species is on it's way out.

If only the lions could take the fur coat off when it's roasting hot, and just put it on when it's freezing cold and pissing rain, then they would have the best of both worlds. 

That's what we've achieved by making shelters and using skins, (or whatever is available for covering). You can sit out the worst of it, and then emerge and endure the heat without having to wear a fur coat.

The date of clothing arriving is a bit of a red herring. It's shelter that I'm talking about, whatever the means. Anything that keeps the rain off. Skins, leaves, grasses whatever. Clothes would probably come much later. 

Without reading the thread, I'm intrigued as to how it got from the topic title to fashion in just 3 page's... 

[zapatos]

2 hours ago, mistermack said:

The date of clothing arriving is a bit of a red herring. It's shelter that I'm talking about, whatever the means. Anything that keeps the rain off. Skins, leaves, grasses whatever. Clothes would probably come much later. 

Is rain really that deadly? 

[TheVat]

You can get a tan, sitting in the English rain.

 

[swansont]

1 hour ago, TheVat said:

You can get a tan, sitting in the English rain.

 

If you’re the walrus
Goo goo g’joob

[mistermack]

2 hours ago, zapatos said:

Is rain really that deadly? 

Well, in the case of humans, you only need to die once, in the first dozen years of life, and your genes will probably be lost to existence. Imagine you're ten, you've got the flu, and you have to live out in the open for a week in Africa in the cold rainy season, naked with no clothes or shelter. How do you think you would do?

There are about 6,400 species of mammal. I can think of less than 20 that don't have a fur coat. And those are either huge, or live underground or in caves. So why do YOU think the 6,380 species all maintain the fur? And of course, you can multiply that, if you add the birds. Feathers do much the same job in the protection against the elements. 

Birds and mammals are both warm blooded, that's the link. 

[CharonY]

13 hours ago, zapatos said:

 

Perhaps a loss of hair eliminated a significant cause of death due to vermin.

 

External parasites are indeed one of the hypotheses. Another one is sexual selection. The others have been previously mentioned.

By taking into account where our ancestors (australopiths) lived it was suggested that heat load reduction is more important when foraging in tropical habitats. There is also a suggestion that bipedalism evolved because of thermoregulatory benefits (https://doi.org/10.1016/j.jhevol.2016.02.006). These were more important to our ancestors as they moved from forest environments into more open habitats. 

Conversely it would mean that clothing likely only became more relevant when moving out of tropical climate zones. There are a range of suggestions on what behavioral adaptations might have occurred to protect from cold, but they appear to be fairly minor, especially concerning our physiological abilities to deal with heat.

So far the strongest evidence we have point toward thermoregulation as one of the major influences. 

 

[zapatos]

5 minutes ago, mistermack said:

Imagine you're ten, you've got the flu, and you have to live out in the open for a week in Africa in the cold rainy season, naked with no clothes or shelter. How do you think you would do?

Imagine you're ten, you have a fever, and you have to live out in the open for a week in Arica in the hot and dry season, covered in hair and no way to cool off. How do you think you would do?

We all have imaginations. Unfortunately they don't really mean anything unless we've got some evidence to back it up.

[CharonY]

15 minutes ago, mistermack said:

There are about 6,400 species of mammal. I can think of less than 20 that don't have a fur coat. And those are either huge, or live underground or in caves. So why do YOU think the 6,380 species all maintain the fur?

So based on your hypothesis, the orangutans who are able to shield themselves form rain would soon be naked? 

Each species history is unique and comparisons would only make sense if we find equivalency in critical aspects. One argument for heat sensitivity of humans is that the human brain is quite large and is very sensitive to overheating. Quite a few animals have for example a carotid rete, which helps cooling the brain especially during bursts of activity. We don't have that, for example. And I will again point to folks living in savannas who often only cover their lower body parts and somehow are still alive.

Many animals in that habitat reduce activity during the day or have some other physiological adaptations to deal with heat. 

[mistermack]

3 minutes ago, CharonY said:

And I will again point to folks living in savannas who often only cover their lower body parts and somehow are still alive.

And do their kids sleep outside in the rain, in the cold rainy season? Some of your posting is sadly lacking in logic. 

[Genady]

I live in tropics, and we have rainy season. The rainy season is wet, but certainly not cold. I often sit under a tree and enjoy the sound and the smell of rain. 

[StringJunky]

53 minutes ago, mistermack said:

And do their kids sleep outside in the rain, in the cold rainy season? Some of your posting is sadly lacking in logic. 

"Tropical monsoon climates have monthly mean temperatures above 18 °C (64 °F) in every month of the year and a dry season. :200–1 Tropical monsoon climates is the intermediate climate between the wet Af (or tropical rainforest climate) and the drier Aw (or tropical savanna climate)."

[mistermack]

Interestingly, the only mammal that I've been able to find, that is in our size range and hairless, that doesn't live in caves or underground, is a weird pig in Sulawesi, the Babirusa, the one with tusks that grow in a huge curve back into their heads. They are mostly hairy, except the population in North Sulawesi, which is mostly hairless. 

I looked up the Sulawesi climate, and the minimum temperature is 23/24 degrees over the whole year. It's a humid island climate, never more than 20 miles from the sea.

[Genady]

Hence, humans originated on a tropical island.

[Ken Fabian]

@mistermack - I am not disagreeing that fire and shelter and maybe clothing too would have been important to the success of early furless hominids, and ever since. It could be a significant reason the furless trait could be sustained rather than taken back out of the gene pool even if, for a time, for some reason or reasons, it was a common variant.

The timing isn't entirely clear but fire use goes back at least that far. Evidence of early shelter making is harder to establish, but very possible, even very likely they were used very early on. A maybe on clothing because shelter and fire would probably be sufficient in a warm climate - as is the case with modern humans, including well outside the warm tropics going by Australian Aborigines, who often wore little more than versions of loincloths, with kids going naked most of the time. Animal skin cloaks and wraps were used in colder places in cold conditions. Oiling the skin of children in Winter was apparently practiced in some colder regions too - I surmise for being water repellent to reduce cold from prolonged time being wet.

It is the use of these as the primary cause for evolving furlessness that I disagree with. But not vehemently; I expect multiple factors at play, not all at the same time.

I think there are some sub-questions that might be answered - was it a progressive loss of fur over many generations? Or was it a distinct furless variant - furless individuals born to furred parents via specific mutation - that swept through the population because it gave survival advantage? Was it sexual selection for attractiveness or natural selection for survivability? Or a dominant genetic mutation that gave no advantage but was survivable, that induced clever tool making problem solvers to rely on and develop better shelter and clothing, that gave a thermo-regulatory advantage far beyond what any fur, even seasonally shedding, can deliver?

And there is still the gain in sensory sensitivity of hairs in humans to explain, that has nothing to do with thermo-regulation. I had thought maybe the sensitivity gain was "spandrel" - the hair shaft size shrank but the follicular nerve supply of much larger hairs remained. Except that Montagna's comparative anatomy makes clear there is a significant increase over what the (larger) hair follicles of related apes have. It may be invisible but that looks as profound a difference between us and our primate relatives as being visibly furless is.

I think not progressive fur loss - because... the furless child. There is no - or very little - variability of furlessness in childhood and if it were a trait subject to incremental change it ought to show variation. Not sexual selection because... the furless child; furlessness has to already be in place in children for preferentially choosing youthful, pre-pubescent furlessness in a sexual partner.

[Ken Fabian]

15 hours ago, Genady said:

I have a question about the timeline. Weren't humans hairless before they first left Eastern Africa? If they were, what was the climate there when the hair was lost?

Their children were presumably furless when humans left Eastern Africa. (I prefer that to hairless, because hairs are still there, just smaller... and with better nerve supply). That every human child is furless in modern humans means it is a homologous trait that goes back to (at the least) the emergence of homo sapiens as a species.

Montagna, approaching it from comparative anatomy asked -

Quote

For that matter, why could we not assume that early Homo had even less coarse body hair than modern man? How do we know that the loss of fur was gradual? Could not the attainment of coarse body hair, especially by some Caucasoids be a recent event? (Caucasoids have, generally, coarser body hairs than the members of most other races.)

Furlessness - the furless child - was part of homo sapiens first. Variations like that greater adult hairiness came later.

15 hours ago, Genady said:

Another question is, does fur give a significant benefit to a child? Does it make a difference in surviving childhood? Considering that human children are very fragile and dependent on adult protection in many respects compared to other mammals.

If it is beneficial to adults it will be beneficial to children. Furred animals pretty much all have furred young. Smaller body size usually means greater heat loss and susceptibility to cold and human babies are especially vulnerable. Also more susceptibility to overheating - which would be more pronounced without the furlessness in combination with greater ability to sweat for cooling. Do children make more internal body heat than adults? They are often very active.

Mistermack mentioned lion cubs dying from cold during wet weather - but having fur that is soaked and stays wet may be a greater risk for hypothermia than having no fur. Similar to wet clothing raising hypothermia risk.

I think it's a case of sometimes it will be a benefit and sometimes it won't. Humans - and our hominid ancestors - were better capable of finding fixes and workarounds than any other species.

Edited December 20, 2022 by Ken Fabian

[Genady]

1 hour ago, Ken Fabian said:

That every human child is furless in modern humans means it is a homologous trait that goes back to (at the least) the emergence of homo sapiens as a species.

Why is it so? Why could not this trait evolve multiple times independently in separate human populations?

[mistermack]

3 hours ago, Ken Fabian said:

The timing isn't entirely clear but fire use goes back at least that far.

I think the timing is not clear at all. The evidence is generally for other stuff, and needs interpretation which ends up as a matter of opinion. There are so many possibilities of how fur was lost that it's not going to be possible to nail it down without some new kind of evidence. Was it sudden, or gradual? Did it happen just once, or several times in seperate populations? Was sex an influence? 

My own instinct says that it happened early, millions of years before fire use, along with a gradual change in climate and environment. Along with the new situation, where our ancestors were habitually walking upright, and their hands were freed to carry stuff. But that's just guesswork.

On the subject of increased nerves feeding hairs, maybe it's a question of leverage. A relatively big hair might give more nerve stimulation than a small fine one, for the same touch event, so the nerves increased to compensate. Just a possibility. 

On lion cubs, their fur obviously does the job, as they generally survive the weather. It's not really similar to wet clothing, it's evolved to not get soaked. There are oil glands to improve moisture repelling, and I believe they have a layer of finer fur that stays dry under an outer layer of coarser fur that guides the water off the body. That's a common model, but I don't know the actual details of lion cub fur.